android仿微信表情雨下落效果的实现方法

public class ItemEmoje { //坐标 public int x; public int y; // 横向偏移 public int offsetX; //纵向偏移 public int offsetY; //缩放 public float scale; //图片资源 public Bitmap bitmap;}

public class RainView extends View { private Paint paint; //图片处理 private Matrix matrix; private Random random; //判断是否运行的，默认没有 private boolean isRun; //表情包集合 private List<ItemEmoje> bitmapList; //表情图片 private int imgResId = R.mipmap.dog; public RainView(Context context) { this(context, null); } public RainView(Context context, @Nullable AttributeSet attrs) { this(context, attrs, 0); } public RainView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); init(); } private void init() { paint = new Paint(); paint.setAntiAlias(true); paint.setFilterBitmap(true); paint.setDither(true); matrix = new Matrix(); random = new Random(); bitmapList = new ArrayList<>(); }}

private void initData() { for (int i = 0; i < 20; i++) { ItemEmoje itemEmoje = new ItemEmoje(); itemEmoje.bitmap = BitmapFactory.decodeResource(getResources(), imgResId); //起始横坐标在[100,getWidth()-100) 之间 itemEmoje.x = random.nextInt(getWidth() - 200) + 100; //起始纵坐标在(-getHeight(),0] 之间，即一开始位于屏幕上方以外 itemEmoje.y = -random.nextInt(getHeight()); //横向偏移[-2,2) ，即左右摇摆区间 itemEmoje.offsetX = random.nextInt(4) - 2; //纵向固定下落12 itemEmoje.offsetY = 12; //缩放比例[0.8,1.2) 之间 itemEmoje.scale = (float) (random.nextInt(40) + 80) / 100f; bitmapList.add(itemEmoje); }}

@Overrideprotected void onDraw(Canvas canvas) { super.onDraw(canvas); if (isRun) { //用于判断表情下落结束，结束即不再进行重绘 boolean isInScreen = false; for (int i = 0; i < bitmapList.size(); i++) {  matrix.reset();  //缩放  matrix.setScale(bitmapList.get(i).scale, bitmapList.get(i).scale);  //下落过程坐标  bitmapList.get(i).x = bitmapList.get(i).x + bitmapList.get(i).offsetX;  bitmapList.get(i).y = bitmapList.get(i).y + bitmapList.get(i).offsetY;  if (bitmapList.get(i).y <= getHeight()) {//当表情仍在视图内，则继续重绘  isInScreen = true;  }  //位移  matrix.postTranslate(bitmapList.get(i).x, bitmapList.get(i).y);  canvas.drawBitmap(bitmapList.get(i).bitmap, matrix, paint); } if (isInScreen) {  postInvalidate(); }else {  release(); } }}/** *释放资源 */private void release(){ if(bitmapList != null && bitmapList.size()>0){ for(ItemEmoje itemEmoje : bitmapList){  if(!itemEmoje.bitmap.isRecycled()){  itemEmoje.bitmap.recycle();  } } bitmapList.clear(); }}

public void start(boolean isRun) { this.isRun = isRun; initData(); postInvalidate();}

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <com.rain.RainView android:id="@+id/testView" android:layout_width="match_parent" android:layout_height="match_parent" /> <Button android:id="@+id/btn_dog" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:text="真・狗头雨・落！" /> <Button android:id="@+id/btn_cake" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_marginLeft="10dp" android:layout_toRightOf="@+id/btn_dog" android:text="蛋糕雨" /></RelativeLayout>

btnCake.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //蛋糕图片 rainView.setImgResId(R.mipmap.cake); rainView.start(true); }});btnDog.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //狗头图片 rainView.setImgResId(R.mipmap.dog); rainView.start(true); }});